Berkeley DB Reference Guide: Transaction Subsystem

Transaction limits

The transaction ID space in Berkeley DB is 2^31, or 2 billion entries.
It is possible that some environments may need to be aware of this
limitation.
Consider an application performing 600 transactions a second for 15
hours a day.
The transaction ID space will run out in roughly 66 days:

2^31 / (600 * 15 * 60 * 60) = 66

Doing only 100 transactions a second exhausts the transaction ID space
in roughly one year.

The transaction ID space is reset each time recovery is run. If you reach
the end of your transaction ID space, shut down your applications and
restart them after running recovery. The most recently allocated
transaction ID is the st_last_txnid value in the transaction
statistics information, and is displayed by the db_stat utility.